We employed the Chavez (1996) COST model to convert the digital
number of the six TM scenes into surface reflectance. The COST
model uses the cosine of the solar zenith angle to approximate the
atmospheric transmittance for the dates and sites which can help
maximize the accuracy. Then, we mosaicked the three reflectance
images of the same year to produce a larger image that covers the
entire study area. To address the spectral disparities between
scenes at adjacent WRS-2 paths (i.e., Path18/Row37 and Path19/
Row37) due to varying acquisition dates, we spectrally match the
overlaying area of the two TMscenes that covers less than 2% of the
entire study site. We then geometrically rectified the mosaicked
images with reference to the 1997 Landsat TM image, which has
already been accurately rectified and georeferenced to the UTM
(Universal Transverse Mercator) map projection (Zone16), NAD83
datum and GRS1980 ellipsoid. The number of ground control points
and resultant average root mean square error (RMSE) are shown in
Table 1. The first-degree polynomial fit was used in image transformation
given the relatively flat terrain relief in this region. The
nearest-neighbor resampling method was applied to avoid
changing the images' original pixel values. Finally, we used the
boundary of the 29-county Atlanta region to subset the image to fit
the study area. Note that in order to account for the possible
georeferenced error, we created a 200 m buffer immediately surrounding
the 29-county polygon that was actually used for the
image subsetting. To ensure the spatial accuracy of the land use/
cover classification with ancillary data, both the street centerline
data and the LandPro data were geometrically rectified with
reference to the mosaicked image.